The present invention relates to a control system for use with heavy duty hydraulic hammers of the type mountable on the boom of construction equipment. More particularly, the present invention provides a control system allowing one to start a heavy duty hydraulic hammer at a reduced impact frequency which is automatically increased to full power after a preselected delay.
Heavy duty hydraulic hammers are well known and used frequently in demolition, mining and construction tasks. These hammers are often mounted at the end of the stick or boom of an excavator. They are supplied with hydraulic fluid under pressure which causes a piston within the hammer to reciprocate, striking a tool, such as a chisel point, which impacts against a workpiece. The piston is forced up by hydraulic fluid with its end compressing gas in a gas chamber. When the piston completes its upward movement, the high pressure fluid is exhausted and the compressed gas drives the piston into the tool. A set amount of hydraulic fluid is required for each upward stroke of the piston.
Heavy duty hydraulic hammers come in various sizes. Smaller units weigh several hundred pounds while larger units can weigh more than 15,000 pounds. These hammers use tool sizes commensurate with their own size and have a rated power capacity commensurate with their size. Hydraulic hammers are used to break up concrete, rock, ore, and the like.
Hydraulic hammers are available from a number of sources commercially. Their design and operation are described in numerous patents including U.S. Pat. No. 3,872,934 to Terada; U.S. Pat. No. 4,034,817 to Okada; U.S. Pat. No. 4,852,664 to Terada; and, U.S. Pat. No. 4,945,998 to Yamanaka.
One type of hydraulic hammer generally comprises a housing containing a piston, a cylinder and a gas chamber at the top of the cylinder. The piston is driven upwardly by hydraulic fluid compressing gas in the gas chamber. When the piston reaches the top of its stroke, the fluid is exhausted and high gas pressure in the gas chamber forcefully moves the piston downwardly. The piston strikes a tool held in the hammer which in turn strikes a workpiece. The power supplied by the high pressure hydraulic fluid is expended in impacting on the workpiece. The impact frequency, the number of impacts per minute, of a hydraulic hammer can be several hundred or several thousand impacts per minute. Each impact involves significant amounts of energy.
While hydraulic hammers generally operate well, problems still exist. When a hammer is operated with the tool not in contact with a workpiece, significant amounts of energy must be absorbed by the hammer itself. Energy is being supplied by the high pressure hydraulic fluid but is not being absorbed by the workpiece. Therefore, significant amounts of energy are absorbed within the hammer, heating it and potentially damaging it. Similar problems occur when the hammer tool is only lightly in contact with a workpiece or in glancing contact with a workpiece. In such situations, the tool is not fully impacting upon a workpiece capable of absorbing energy. Energy is absorbed in the hammer to its detriment. This situation is so common it has a name. Hammers operating when not engaged against a workpiece are often said to be blank firing.
Applicant has found that a significant portion of blank firing occurs within the first several seconds of hammer actuation. Thus, blank firing often occurs when a hammer is first positioned on a workpiece and the hammer either slides off resulting in blank firing or quickly breaks the workpiece resulting in blank firing. Often, several impact in a glancing or lightly engaged mode are required before the hammer tool can dig into and grip a workpiece sufficient to supply adequate back pressure to load a hammer. If done at full frequency, the hammer is hard to control and will bounce of a workpiece before it can engage it and grip it.
In accordance with the present invention, a control system for a heavy duty hydraulic hammer is provided in which the hammer may be operated in a low frequency, or slow mode, for a selected initial period whenever the hammer is actuated.
Yet further in accordance with the invention, the initial period of low frequency operation is selectable by an operator in an excavator cab by means of a hand operated control.
Still further in accordance with the invention, a mode switch is provided in the control system allowing an operator to select the low frequency start feature or a constant low frequency operation setting.
Yet further in accordance with the invention, a control system is provided which selectively provides hydraulic fluid flow to a heavy duty hydraulic hammer at a rate considerably reduced from its normal operating rate whereby low frequency operation is achieved.
Still further in accordance with the invention, an electro-hydraulic hammer control system is provided which allows a user to select from the cab of an excavator between an initial low frequency operation for a selected period of time, constant low frequency operation, full power start operation, and no operation at all.
It is a principal object of the present invention to provide a control system for a heavy duty hydraulic hammer which minimizes blank firing.
It is another object of the present invention to provide a control system for a heavy duty hydraulic hammer which allows an operator to establish a workpiece grip point at low frequency when working on larger, difficult workpieces.
It is yet another object of the present invention to provide a control system for a heavy duty hydraulic hammer allowing an operator to select a period of initial low frequency operation prior to automatic full power operation with simple controls and a cab.
It is still another object of the present invention to provide a versatile control system for a heavy duty hydraulic hammer which is robust, easy to use, and easy to install into existing excavators.